1. Field of the Invention
The present invention relates, in general, to stereoscopic image projection, and, more particularly, to systems and methods for producing stereoscopic images for three-dimensional (3D) projection from a two-dimensional (2D) image source such as a 2D cell animation and/or a live action film.
2. Relevant Background
Recently, there has been a renewed demand for 3D entertainment including movies, video games, animation, and the like that are displayed or projected in 3D format. The images or image frames used to produce such a 3D output are often called stereoscopic images or a stereoscopic image stream because the 3D effect is due to stereoscopic perception by the viewer. A frame is a single image at a specific point in time, and motion or animation is achieved by showing many frames per second (fps) such as 24 to 30 fps. Stereoscopic perception results from the presentation of two images or frames representing horizontally separated perspectives with one or more objects (or visible features of the objects) slightly offset to the viewer's left and right eyes. The amount of offset between the elements of left and right eye images determines the depth at which the elements are perceived in the resulting stereo image. An object appears to protrude toward the observer and away from the neutral plane or screen when the position or coordinates of the left eye image are crossed with those of the right eye image (e.g., negative parallax). In contrast, an object appears to recede or be behind the screen when the position or coordinates of the left eye image and the right image are not crossed (e.g., positive parallax).
Many techniques have been devised and developed for projecting stereoscopic images to achieve a 3D effect. One technique is to provide left and right eye images for a single, offset two-dimensional image and displaying them alternately, e.g., using 3D switching or similar devices. A viewer is provided with liquid crystal shuttered spectacles to view the left and the right eye images. The shuttered spectacles are synchronized with the display signal to admit a corresponding image one eye at a time. More specifically, the shutter for the right eye is opened when the right eye image is displayed and the liquid crystal shutter for the left eye is opened when the left eye image is displayed. In this way, the observer's brain merges or fuses the left and right eye images to create the perception of depth.
Another technique for providing stereoscopic view is the use of anaglyph. An anaglyph is an image generally consisting of two distinctly colored, and preferably, complementary colored, images. The theory of anaglyph is the same as the technique described above in which the observer is provided separate left and right eye images, and the horizontal offset in the images provides the illusion of depth. The observer views the anaglyph consisting of two images of the same object in two different colors, such as red and blue-green, and shifted horizontally. The observer wearing anaglyph spectacles views the images through lenses of matching colors. In this manner, the observer sees, for example, only the blue-green tinted image with the blue-green lens, and only the red tinted image with the red lens, thus providing separate images to each eye. The advantages of this implementation are that the cost of anaglyph spectacles is lower than that of liquid crystal shuttered spectacles and there is no need for providing an external signal to synchronize the anaglyph spectacles. In other 3D projection systems, the viewer may be provided glasses with differing polarization such that the alternating right-left eye images are seen with the appropriate eye based on the displayed stereoscopic images having appropriate polarization. Other devices have been produced in which the images are provided to the viewer concurrently with a right eye image stream provided to the right eye and a left eye image stream provided to the left eye. Still other devices produce an auto-stereoscopic display via stereoscopic conversion from an input color image and a disparity map, which typically has been created based on offset right and left eye images. While these display or projection systems may differ, each typically requires a stereographic image as input in which a left eye image and a slightly offset right eye image are provided to create a presentation with the appearance of depth.
Digital animation that has been modeled in 3D can readily be converted into stereo or into stereoscopic image streams by filming or shooting the previously rendered frames or shots with a set of stereo cameras (e.g., a left eye camera and a horizontally offset right eye camera). However, there are a large number of 2D animated movies and other 2D media such as live action footage or motion pictures available for use in creating 3D entertainment such as 3D animated films. For example, traditional 2D cell animation has largely migrated to or been converted to the digital world, and the image levels to be composited into a final image have been stored either in bitmap, vector, or a hybrid format. This is true regardless of whether the drawings were initially created using a computer or on conventional media that was later digitized through scanning or other methods. The availability of the animation and other image sources in this digital form lends itself toward generating a stereoscopic image from the 2D or monoscopic image, but existing 2D-to-3D methods have not been widely accepted by the entertainment industry.
There are a number of methods presently used to transform flat or 2D drawings or images into 3D images. One method may be thought of as the horizontal shift method and involves isolating several important objects in the image field and shifting these objects horizontally. The shifted image is presented as an alternate eye view to the primary or original eye view, and a depth is perceptible between the shifted objects. The result has not been entirely successful, though, with many believing that 2D cell animation should not be transformed into and released as a 3D product using this method because the objects lack volume or individual depth and appear to be cardboard cutouts or flat objects presented in distinct planes (e.g., similar to a pop up book or the like in each frame). Other algorithms are available that address this problem by applying the 2D image such as a 2D drawing as a surface onto a 3D model. Unfortunately, the success of this technique depends on the creation of an accurate 3D model, and the results are often less than desirable. These and other features of the modeling tools have proven complex and difficult to use as well as being relatively costly and time consuming.
Hence, there remains a need for methods for transforming flat or 2D objects into 3D objects for use in creating stereoscopic images. Preferably such methods would provide a relatively automated technique for creating an alternate eye image useful for providing objects that appear to have volume or individual depth as well as providing a depth perception to a viewer (e.g., do not appear as mere planar objects or cardboard cutouts).